1. Field of the Invention
The present invention relates to a non-volatile semiconductor memory device, and more particularly to a data write circuit employing a high write voltage in such a non-volatile semiconductor memory device.
2. Description of the Prior Art
An electrically programmable, non-volatile read-only memory (referred to as an EPROM) has a plurality of memory cells arranged in a matrix of word lines and digit lines, and data is written into a selected memory cell by applying a high voltage thereto through a selected word line or a selected digit line. In a writing operation, it is required that the high voltage be applied to the selected word line or digit line only, and that all the other non-selected word lines or digit lines be grounded or clamped at a fixed low potential. This wastes a large amount of current flowing through all the non-selected word or digit lines to the ground or the fixed potential source during the data writing operation period. Such a large power consumption is one of the shortcomings of the prior art EPROM.
The large amount of current flowing from a high voltage terminal to which the high voltage is supplied toward the ground or the low potential source causes a voltage level drop at the high voltage terminal. Taking into consideration in that the high voltage level which is sufficient to write data to the respective memory cells is not constant because of deviations in semiconductor fabrication, the dropped high voltage sometimes fails to correctly write data into some memory cells. This is another drawback of the conventional EPROM. This drawback may be resolved by providing the memory chip with a plurality of high voltage terminals to enable the application of a high voltage to the selected word or digit line. However, this is not practical, because the number of terminals is limited on the memory chip and it is impossible to assign many terminals for supplying a high voltage.